(vi) Radio-Nuclide Effects: -
The
increasing development of nuclear energy is producing more radioactive wastes
to be disposed of into the environment, and it contains various radionuclides
with long half lives. The nuclear waste into the atmosphere may enter water by
a settling process by rains. Solid waste (nuclear) filled in containers is
dumped into sea bed. The corrosive action of sea water may cause leakage of radioactive
waste in water and it may pose health hazards. Radionuclides can enter the
human body through dusts and aerosols and can also be absorbed by plants and
animals.
(vii) Eutrophication of Lakes: -
The condition
of excessive growth of plants, both attached and planktonic, in a water body is
called ‘Eutrophication’. It is a natural process of aging of a water body
(particularly lakes). It is a result of a very slow process of natural
sedimentation of microscopic organisms which takes geologic times to complete.
The completion of the process results in the extinction of the water body
(lake).
Various process of water treatment: -
1. Preliminary Treatment: -
Preliminary Treatment is carried out for
the removal of the floating materials (such as leaves of trees, pieces of rags,
paper, wood, dead animals, etc.), the heavy settleable inorganic solids (such
as sand, grit, etc.) and the fats, oils and greases from the waste water.
Preliminary treatment reduces the BOD (Biochemical Oxygen Demand) about 15-30%,
the solids about 20-40%, and the bacterial load about 10-20%.
2.
Primary Treatment: -
Primary Treatment is carried out
for the removal of large suspended organic solids present in the waste water.
Primary treatment reduces the BOD about 30-35%, the solids about 40-60% and the
bacterial load about 20-75%. The primary treatment is usually accomplished by
sedimentation.
3.
Secondary Or Biological Treatment: -
Secondary treatment is carried out for the
removal of fine suspended and dissolved organic material present in the
effluent from the primary treatment unit, by means of biological flocculation
and precipitation, and then by settling out (i.e., secondary sedimentation). In
the secondary or biological treatment units, bacteria and other micro-organisms
decompose the fine organic matter to produce a clearer effluent.
4.
Tertiary Or Final Treatment: -
This treatment is also called advanced treatment.
The final treatment, which is normally carried out by chlorination (i.e.
disinfection), is generally not carried out for disposal of sewage in water
bodies. But, it may be adopted when the outfall of sewage (in the river/stream)
is very near to the water intake of some nearby town on the down stream side of
the river / stream. The sewage treatment is, therefore, usually confined up to
secondary treatment only.
Layout
Of Water Treatment Plant: -
Figure a. shows the process flow sheet of
a conventional sewage treatment plant; in which trickling filters use is
suitable for small and medium cities, while activated sludge process is
suitable for larger cities. Fig b, c and d show the process flow sheets using
oxidation ditch, aerated lagoon, and stabilization pond respectively, suitable
for a village or a colony.
